1. Field of The Invention
The present invention relates to a control apparatus for a waste gate valve of a supercharger in an internal combustion engine, more particularly to an apparatus capable of controlling the waste gate valve accurately without providing any special sensor for detecting the temperature of intake air into the internal combustion engine.
2. Description of The Related Art
As is well known, a supercharger for an internal combustion engine has a turbine, which is provided within an exhaust pipe and operated by exhaust gas from the engine, and a compressor, which is provided within an intake pipe and operably coupled with the turbine. The engine is supercharged with air by the compressor driven by the turbine so that the charging efficiency of intake air in the engine is much improved.
In such a supercharger, there is usually provided a waste gate valve in a path which makes a part of the exhaust gas by-pass the turbine of the supercharger. The excessive increase of the supercharging pressure during the high speed operation of the engine is suppressed by controlling the opening of the waste gate valve in accordance with the pressure within the intake pipe.
The control of such a waste gate valve is carried out by an electronic control device including a microprocessor. A typical one of examples of such an electronic control device is disclosed in Japanese Patent Laid-open Publication No. 60-81425 (published May 9, 1985). In this prior art, attention is paid to the fact that, although the charging efficiency depends on the intake pressure, which is pressure within an intake pipe in the down stream of a throttle valve, the intake pressure is greatly influenced by the supercharging pressure in the range of the large opening of the throttle valve.
Then, according to the prior art, an actual value of the intake pressure is controlled following a desired value thereof, which is determined in accordance with the number N of revolutions of the engine and the temperature T.sub.a of the intake air. To this end, an apparatus according to the prior art has a memory map from which the desired value of the intake pressure is read out in response to N and T.sub.a detected by respective sensors.
As described above, in the prior art, there was necessary a sensor exclusively used for detecting the temperature T.sub.a of the intake air, with the result that the number of sensors is increased. Usually, in an electronic control apparatus of this kind, a great concern must be paid about the utilization efficiency of equipment included in the apparatus. The increase in the number of sensors deteriorates this utilization efficiency.